绘图的一部分的开放的gl纹理
我正在试图只绘制我的精灵表的一部分。 但它只是缩放图像，没有绘制图像宽度的1/3。 我怎样才能裁剪图像，所以只有1/3显示。 文本在下面（ios 7，opengl es 2） – （GLKMatrix4）modelMatrix {
GLKMatrix4 modelMatrix = GLKMatrix4Identity; modelMatrix = GLKMatrix4Translate(modelMatrix, x, y, 0); return modelMatrix; } - (void)setSprite:(NSString *)fileName effect:(GLKBaseEffect *)newEffect { // 1 self.effect = newEffect; // 2 NSDictionary * options = [NSDictionary dictionaryWithObjectsAndKeys: [NSNumber numberWithBool:YES], GLKTextureLoaderOriginBottomLeft, nil]; // 3 NSError * error; NSString *path = [[NSBundle mainBundle] pathForResource:fileName ofType:nil]; // 4 self.textureInfo = [GLKTextureLoader textureWithContentsOfFile:path options:options error:&error]; if (self.textureInfo == nil) { NSLog(@"Error loading file: %@", [error localizedDescription]); return ; } TexturedQuad newQuad; newQuad.bl.geometryVertex = CGPointMake(0, 0); newQuad.br.geometryVertex = CGPointMake(self.textureInfo.width, 0); newQuad.tl.geometryVertex = CGPointMake(0, self.textureInfo.height); newQuad.tr.geometryVertex = CGPointMake(self.textureInfo.width, self.textureInfo.height); newQuad.bl.textureVertex = CGPointMake(0, 1); newQuad.br.textureVertex = CGPointMake(1, 1); newQuad.tl.textureVertex = CGPointMake(0, 0); newQuad.tr.textureVertex = CGPointMake(1, 0); self.quad = newQuad; } - (void)render { // 1 self.effect.texture2d0.name = self.textureInfo.name; self.effect.texture2d0.enabled = YES; // 2 y++; self.effect.transform.modelviewMatrix = self.modelMatrix; [self.effect prepareToDraw]; // 3 glEnableVertexAttribArray(GLKVertexAttribPosition); glEnableVertexAttribArray(GLKVertexAttribTexCoord0); // 4 TexturedQuad q; q.bl.textureVertex = CGPointMake(0, 1); q.br.textureVertex = CGPointMake(1, 1); q.tl.textureVertex = CGPointMake(0, 0); q.tr.textureVertex = CGPointMake(1, 0); q.bl.geometryVertex = CGPointMake(0, 0); q.br.geometryVertex = CGPointMake(self.textureInfo.width/3, 0); q.tl.geometryVertex = CGPointMake(0, self.textureInfo.height); q.tr.geometryVertex = CGPointMake(self.textureInfo.width/3, self.textureInfo.height); long offset2 =(long)&q; //long offset = (long)&_quad; glVertexAttribPointer(GLKVertexAttribPosition, 2, GL_FLOAT, GL_FALSE, sizeof(TexturedVertex), (void *) (offset2 + offsetof(TexturedVertex, geometryVertex))); glVertexAttribPointer(GLKVertexAttribTexCoord0, 2, GL_FLOAT, GL_FALSE, sizeof(TexturedVertex), (void *) (offset2 + offsetof(TexturedVertex, textureVertex))); // 5 glDrawArrays(GL_TRIANGLE_STRIP, 0, 4); }
更新：TexturedQuad newQuad; newQuad.bl.geometryVertex = CGPointMake（0，0）; newQuad.br.geometryVertex = CGPointMake（self.textureInfo.width / 3，0）; newQuad.tl.geometryVertex = CGPointMake（0，self.textureInfo.height）; newQuad.tr.geometryVertex = CGPointMake（self.textureInfo.width / 3，self.textureInfo.height）;
newQuad.bl.textureVertex = CGPointMake(0, 1); newQuad.br.textureVertex = CGPointMake(.3, 1); newQuad.tl.textureVertex = CGPointMake(0, 0); newQuad.tr.textureVertex = CGPointMake(.3, 0);
这就是纹理坐标。 你的'textureVertex'指定你的纹理的全部尺寸（0.0到1.0）映射到四边形。 您需要将其中一些值更改为1/3或2/3。 例如：
newQuad.bl.textureVertex = CGPointMake(0, 0.33); newQuad.br.textureVertex = CGPointMake(1, 1); newQuad.tl.textureVertex = CGPointMake(0, 0.33); newQuad.tr.textureVertex = CGPointMake(1, 0);